1. Field of the Invention
The present invention relates to a so called spin-valve type thin film element in which electric resistance is changed by the relation between the direction of magnetization of a pinned magnetic layer and the direction of magnetization of a free magnetic layer that is influenced by the external magnetic field, especially to a spin valve type thin film element in which induced magnetic anisotropy of the free magnetic layer is made to be generated along a proper direction using an antiferromagnetic layer that causes an exchange coupling by applying a heat treatment, and its manufacturing method.
2. Description of the Related Art
FIG. 7 is a cross section in the vicinity of the ABS surface of a conventional spin-valve type thin film element for sensing recording magnetic field from a recording medium such as a hard disk.
An underlayer 6, a free magnetic layer 4, a non-magnetic electrically conductive layer 3, a pinned magnetic layer 2, an antiferromagnetic layer 10 and a protective layer 7 are continuously formed from the bottom to the top in this spin-valve type thin film element, on both side S of which hard magnetic bias layers 5, 5 are formed.
Usually, a Fe--Mn (iron--manganese) alloy film is used for the antiferromagnetic layer 10, a Ni--Fe (nickel--iron) alloy film is used for the pinned magnetic layer 2 and free magnetic layer 4, a Cu (copper) layer film is used for the electrically conductive layer 3 and a Co--Pt (cobalt--platinum) alloy film is used for the hard magnetic bias layers 5, 5. The underlayer 6 and protective layer 7 are formed of a non-magnetic material such as Ta (tantalum).
An exchange anisotropic magnetic field due to exchange coupling is created, without applying any heat treatment, at the interface between the pinned magnetic layer 2 and antiferromagnetic layer 10 by depositing the films of the pinned magnetic layer 2 and antiferromagnetic layer 10 while applying a magnetic field along the Y-direction (the height direction; the direction of the leakage magnetic field from recording media) since the antiferromagnetic layer 10 is formed of the Fe--Mn alloy film, thereby fixing magnetization of the pinned magnetic layer 2 along the Y-direction forming a single magnetic domain caused by the exchange anisotropic magnetic field.
The hard magnetic bias layers 5, 5 are magnetized along the X-direction (the track width direction), thereby allowing magnetization of the free magnetic layer 4 to be aligned along the X-direction.
The first step for producing the spin-valve type thin film element shown in FIG. 7 comprises depositing six layers from the underlayer 6 to the protective layer 7 (referred to a laminated body hereinafter) while applying a magnetic field along the Y-direction.
An exchange anisotropic magnetic field is generated at the interface between the pinned magnetic field 2 and antiferromagnetic layer 10 in this deposition step, fixing magnetization of the pinned magnetic field 2 along the Y-direction.
In the next step, the laminated body is processed to a prescribed shape by, for example, ion milling, followed by depositing the hard bias layers 5, 5 and conductive layers 8, 8 on both sides of the laminated body.
A stationary current (a sensing current) is imparted from the conductive layer 8, 8 to the pinned magnetic field 2, non-magnetic conductive layer 3 and free magnetic layer 4 in this spin-valve type thin film element. While the travelling direction of the recording medium such as a hard disk is along the Z-direction, the magnetization direction of the free magnetic layer 4 is turned from the X-direction to the Y-direction when the leakage magnetic field from the recording medium is applied along the Y-direction. Electric resistance is fluctuated depending on the relation between the variation of the magnetization direction within this free magnetic layer 4 and pinned magnetization direction in the pinned magnetic field 2, sensing the leakage magnetic field from the recording medium due to voltage changes based on the fluctuation of the electric resistance.
However, because the laminated body from the underlayer 6 to the protective layer 7 is deposited while applying a magnetic field along the Y-direction in the spin-valve type thin film element shown in FIG. 7, an inductive magnetic anisotropy is induced along the Y-direction in the free magnetic layer 4, allowing the Y-direction of the free magnetic layer 4 to be an easy axis of magnetization.
Accordingly, the magnetization of the free magnetic layer 4 when the laminated body has been deposited is aligned along the Y-direction, forming a large coercive force along the Y-direction.
After depositing the laminated body, hard bias layers 5 are deposited on both sides of the laminated body to align magnetization of the free magnetic layer 4 along the X-direction. However, magnetization can not be properly aligned along the X-direction because not only bias magnetic field but also inductive magnetic anisotropy is applied to the free magnetic layer 4, thereby deteriorating reproduction characteristic in that Barkhausen noises are liable to be generated.
Japanese Unexamined Patent Publication No. 9-92908 describes an invention titled "Method for Producing Magnetoresistive Element" that discloses a different production method from those as hitherto described.
The spin-valve type thin film element described in this publication is, like those as shown in FIG. 7, composed of a free magnetic layer 4 (described as a "functional film" in the publication), non-magnetic conductive layer 3 (described as a "non-magnetic film" in the publication), a pinned magnetic layer 2 (described as a "magnetization pinning film" in the publication) and an antiferromagnetic layer 10 (described as an "antiferromagnetic film" in the patent publication) from the bottom to the top.
At first, the magnetic layer 4 is deposited while applying a magnetic field along the X-direction (the track width direction; described as "magnetic field impressing direction 21A" in the foregoing patent publication) shown in FIG. 7 using a sputtering apparatus that are able to rotate its substrate holder (the reference numeral 67 shown in FIG. 6 and FIG. 10 in the foregoing patent publication) by an angle of 90 degree in depositing each layer described above.
Then, the substrate holder is rotated by an angle of 90 degree and, while applying a magnetic field along the Y-direction shown in FIG. 7 (the height direction; described as "magnetic field impressing direction 21B" in the foregoing patent publication), a non-magnetic conductive layer 3, a pinned magnetic layer 2 and an antiferromagnetic layer 10 are deposited on the free magnetic layer 4.
Since the antiferromagnetic layer 10 described above are formed of a Fe--Mn alloy film, an exchange coupling is generated during deposition in the magnetic field, therefore magnetization of the pinned magnetic layer is fixed along the Y-direction forming a single magnetic domain.
The X-direction of the free magnetic layer 4 is described to be made as an easy axis of magnetization in the production method described in the foregoing patent publication because the free magnetic layer 4 is deposited by applying a magnetic field along the X-direction.
However, it is thought to be difficult to allow the X-direction of the free magnetic layer 4 to be the direction of the easy axis of magnetization by the following reasons in the production method as described in the foregoing publication when the anti-ferromagnetic layer 10, which acquires an exchange coupling with the pinned magnetic layer 2 at the interface by applying a heat treatment under a magnetic field along the Y-direction (the height direction), is used.
Because the free magnetic layer 4 is deposited while applying a magnetic field along the X-direction, an inductive magnetic anisotropy along the X-direction is in the free magnetic layer 4 immediately after depositing the free magnetic layer 4, thereby the free magnetic layer 4 is magnetized with its X-direction to be an easy axis of magnetization.
Meanwhile, since the non-magnetic conductive layer 3, the pinned magnetic layer 2 and the antiferromagnetic layer 10 formed on the free magnetic layer 4 is deposited by applying a magnetic field along the Y-direction, the magnetization direction of the free magnetic layer 4 is directed along the Y-direction during deposition of the three layers described above and the pinned magnetic layer 2 is endowed with inductive magnetic anisotropy along the Y-direction.
A magnetic inter-layer interaction to align the magnetization directions with each other is applied between the pinned magnetic layer 2 and free magnetic layer 4 confronting via the very thin non-magnetic conductive layer 3 when the pinned magnetic layer 2 is deposited while being endowed with inductive magnetic anisotropy along the Y-direction. Accordingly, inductive magnetic anisotropy of the free magnetic layer 4 that has been applied along the X-direction is distorted to some extent due to deposition of the pinned magnetic layer 2 immediately after deposition of the free magnetic layer 4.
The fact that inductive magnetic anisotropy along the X-direction is distorted to some extent corresponds to a phenomenon wherein the X-component of magnetic anisotropy is reduced as a result of added vectors along the X-direction and Y-direction along with turning the direction of inductive magnetic anisotropy of the free magnetic layer 4 from the X-direction to the Y-direction by a small degree, because inductive magnetic anisotropy along the Y-direction is also applied to the free magnetic layer 4 from the pinned magnetic layer 2.
When the antiferromagnetic layer 10, which generates an exchange coupling at the interface between the antiferromagnetic layer 10 and pinned magnetic layer 2 by applying a heat treatment under a magnetic field along the Y-direction, is used, the layer is subjected to the heat treatment while magnetization directions of the free magnetic layer 4 and pinned magnetic layer 2 are aligned along the Y-direction (when magnetization along the Y-direction is saturated). Since inductive magnetic anisotropy induced by the heat treatment is added to the free magnetic layer 4 along the Y-direction, inductive magnetic anisotropy of the free magnetic layer 4, being applied along the X-direction immediately after depositing the free magnetic layer 4, is distorted to some extent from the X-direction by applying a heat treatment.
Accordingly, inductive magnetic anisotropy of the free magnetic layer 4 before the heat treatment, or when deposition of the entire laminated body has been completed, should be made to be as hardly distorted from the X-direction as possible when the ferromagnetic layer, which causes an exchange coupling at the interface with the pinned magnetic layer 2 by applying a heat treatment under a magnetic field along the Y-direction, is used. Therefore, the deposition method in which a magnetic field is applied along the Y-direction is not preferable.
It is necessary in the invention described in the foregoing patent publication to newly produce a sputtering apparatus being able to rotate the substrate holder by an angle of 90 degree. Therefore, existing sputtering apparatus being able to apply the magnetic field only along one direction can not be used, imposing construction of separate facilities.